Polyvinyl acetate binder for crystalline explosive



United States Patent 3,428,502 POLYVINYL ACETATE BINDER FOR CRYSTALLINE EXPLOSIVE William L. Evans, Blackwood, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 481,150, Aug. 19, 1965. This application Oct. 25, 1966, Ser. No. 589,199

US. Cl. 149--19 Int. Cl. C06b 15/02, 3/00 40 Claims ABSTRACT OF THE DISCLOSURE An explosive composition comprising 45 to 85% particulate crystalline explosive and at least 15% polymeric binder comprising 5 to 55% of a vinyl acetate-based copolymer made from 50 to 99 mole percent vinyl acetate and, preferably, the composition contains a polymeric metallocarboxylate elastomer.

It has long been considered desirable in the art of explosives to provide detonating explosive compositions which not only are sensitive to actuation by standard explosive initiators, e.g., detonators such as blasting caps or boosters, yet relatively insensitive to inadvertent actuation by such influences as impact, stray electric discharges, fire, and friction, but also meet such requirements as dimensional stability under stress, water-resistance, good flexibility even at extremely high and extremely low temperatures, and storage stability for periods up to several years. However, only in recent years has there been any appreciable success in this field, particularly in terms of formulating compositions able to maintain these desired physical and explosive characteristics over a wide range of environmental conditions, Explosive compositions of this type basically comprise a crystalline, cap-sensitive detonating composition in a binder or matrix of one of several polymeric, elastomeric binders. However these explosive compositions suffer from one or more deficiencies. For example, several of the previously used combinations of explosive and binder necessitate the use of an explosive of specified small particle size to assure propagation in thin sheets; a binder containing explosives must in many instances be cured at relatively high temperatures; many of the binders previously used must be polymerized from the fluid state and a rather high exotherm develops on polymerization. Then, too, many processes for making the compositions containing an explosive and binder require the employment of volatile, toxic and/or flammable solvents. Furthermore, although many explosive compositions produced following the teachings of the art do have many satisfactory, desirable explosive characteristics, the compositions have limited toughness at ordinary temperatures, and even further reduced toughness at elevated temperatures. This deficiency in physical characteristics is demonstrated, for example, by the ease with which the compositions are severed (cut-through) by reinforcing members under tension and the loss of tensile strength at elevated temperatures.

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It has now been discovered that certain explosive compositions can be easily formed into self-supporting, dimensionally stable, flexible articles which maintain desirable physical and explosive properties even at extreme- 1y .high and low temperatures. The novel explosive compositions comprise uniform blends by weight, of total composition, of about from 45 to 85 preferably about 55 to of a particulate cap-sensitive crystalline explosive and at least about 15% polymeric binder therefor, said binder comprising, based on the total composition, about from 5 to 55% of a vinyl acetate co-, preferably ter-polymer, 0 to about 50%, and preferably 0 to about 35%, of a polymeric metallocarboxylate and 0 to about 10%, and preferably 0 to about 8%, of a polyurethane elastomer, or mixtures thereof, the total binder comprising 15 to 55 by weight of the total composition. The vinyl acetate copolymer can contain crotonic acid or an alkyl or hydroxyalkyl ester thereof wherein the alkyl groups contain 1 to 8 carbon atoms. The copolymer can also contain hydroxyalkyl acrylate, e.g., lower alkyl acrylates wherein the alkyl groups contain from 1 to 8 carbon atoms, preferably hydroxyethyl acrylate thereby forming a terpolymer of vinyl acetate. The polymeric metallocarboxylate copolymer is a reaction product of a polyvalent metal ion with a copolymer of about from 50 to by weight of a butadiene and about from 10 to 45% of an acrylic nitrile and suflicient acrylic acid to provide about from 0.001 to 0.3 carboxyl equivalents per 100 parts by weight of said butadiene-acrylic nitrile copolymer.

The present explosive composition containing a vinyl acetate coor terpolymer can contain up to 20 by weight, plasticizer. The presence of plasticizer increases the flexibility of the explosive composition. Such plasticizers preferably are phosphate or carboxylate esters. In addition conventional antioxidants and dyes which are inert in the system can be incorporated, in minor proportions, e.g., up to about 2% based on total weight of the composition.

The explosive compositions of the invention are prepared by mixing an aqueous dispersion of, by weight, about from 45 to preferably about 55 to 75%, of a particulate cap-sensitive crystalline explosive and about from 5 to 55 of the vinyl acetate copolymer, and preferably a vinyl acetate-crotonate-hydroxyalkyl acrylate terpolymer, from 0 to about 10% of a liquid polyurethane or from about 0 to 50% of an elastomer which is the reaction product of butadiene, acrylonitrile and sufficient amount of acrylic acid providing about from 0.001 to 0.3 carboxyl equivalents per parts by weight of copolymer, a source of polyvalent metal ions in an amount chemically equivalent to about 0.5 to 2 times the carboxyl content of the butadiene-acrylic nitrile copolymer and drying the resulting explosive composition. As noted above, the vinyl acetate based copolymer can consistitute 5 to 55 preferably 5 to 15 and most preferably 5 to 10% of the total weight of the composition. After the ingredients are mixed the composition is dried. When the composition is dried, water is removed and curing accelerated. The resulting dried explosive composition can be shaped, e.g., into blocks, sheets, tubes or rods and suitable reinforcing means, such as nylon yarn, can be incorporated in the explosive composition preferably during the shaping procedure, for example in forming rods the explosive is extruded around said reinforcing means, e.g., the nylon yarn.

Exemplary particulate, cap-sensitive high explosive suitable for incorporation in the compositions of the present invention include nitrates such as pentaerythritol tetranitrate (PETN) and mannitol hexanitrate, nitramines such as cyclotrimethylenetrinitramine (RDX), cyclotetramethylene-tetranitramine (HMX) and trinitrophenyl methylnitramine (tetryl), aromatic nitro compounds such as trinitrotoluene (TNT), diazidodinitro phenol, as well as other cap-sensitive particulate high explosives such as picryl sulfone, tetranitrodibenzo 1,3a,4,6a tetraazapentalene (Tacot), bistrinitroethylurea, lead azide, hexamethylenetriperoxydiamine, and potassium dinitroacetonitrile. The preferred explosives 'used in the composition are PETN, R'DX, and HMX. The explosive component obviously should be compatible with other ingredients of the composition under processing, handling and storage conditions. The particle size of the high explosive is not particularly critical in the compositions of this invention. However, for ease of incorporating the particulate explosive in the elastomeric matrix, particles which pass an 80 mesh (US. Standard sieve), which are smaller than about 200 microns, are preferred. In general, superior initiation sensitiveness is achieved when the average particle size is below about 100 microns, preferably about from 1 to 75 microns. (Average particle size, as used herein, means weight average particle size, as calculated from standard sieve analysis values and from microscopic measurement values for particles generally smaller than the standard 325-mesh US. Standard sieve apertures of 43-44 microns.) As indicated above the concentration or loading of cap-sensitive explosive will generally be about from 45 to 85% of the total weight of the composition. Concentrations of explosives appreciably below this range, in addition to imparting lower explosive strengths per unit weight of composition, make the compositions increasingly insensitive to initiation. Also, even when suitably initiated, such low-concentration compositions often fail to propagate a detonation, or the detonation may be propagated at low velocity. On the other hand, explosive loadings above about 85% cause the compositions to be increasingly diflicult to mix and shape and at the same time tend to impart less than optimum physical characteristics. For optimum results the particulate explosive constitutes about from 55 to 75% of the weight of the composition weight. Accordingly this latter range of explosive concentration is particularly preferred.

Vinyl acetate-based copolymer elastomers which are suitable for preparing the compositions of this invention and constitute at least a portion of the binding matrix are formed by reacting from 50-99 mole percent vinyl ace tate, up to about 45 mole percent of a hydroxyalkyl acrylate, preferably a hydroxyethyl acrylate, and 1 to mole percent, and preferably 2 to 5 mole percent, of crotonic acid or an alkyl or hydroxyalkyl ester of crotonic acid wherein the alkyl group can contain from 1 to 8 carbon atoms. Representative, self-curing, crosslinkable terpolymers of the type identified above are described in U.-S. 3,208,963. Suitable products can be obtained when the vinyl acetate-based copolymer constitutes the reaction products of 90 to 99 mole percent vinyl acetate and the balance crotonic acid or an ester thereof as described above. The toughness and flexibility of the cured copolymers and consequently of explosive compositions based on these copolymers can be controlled by varying the amount of hydroxyalkyl acrylate ester present therein, flexibility increasing with the increasing concentration of the hydroxyalkyl acrylate. Another method by which the flexibility of the composition can be varied is by physically blending the copolymer with a water-soluble homopolymer of polyvinyl acetate, whereby the flexibility of the compatible blend varies inversely in accordance with the amount ofvinyl acetate added. The vinyl acetate homopolyrner may contain up to 20% by Weight of acetate groups, and the concentration of polyvinyl acetate which can be used for this purpose varied from about 20- 80%, based on the total weight of copolymer and vinyl acetate present in the resulting blend.

The crosslinking (curing) of these copolymers is influenced by heat, aging, and/ or catalyst. The ability of the polymers to crosslink depends upon the particular hydroxyalkyl acrylate ester which is used. For example, when hydroxyethyl acrylate is used the terpolymer will crosslink either on prolonged aging, and/or by the application of moderate heating, e.g., up to about C. Catalysts also can be employed to accelerate crosslinking of the copolymers. Catalysts, if needed, are generally employed in amounts of about from 0.5-5.0%, based on weight of the copolymer. Suitable catalysts are those of the acidic type including nonoxidizing inorganic acids such as phosphoric and hydrochloric acids; non-volatile organic acids such as oxalic, fumaric, citric and p-toluene sulfonic acids; and acidic salts such as ammonium citrate, ammonium oxalate, ammonium chloride, ferric chloride, chromic nitrate, chromic chloride, chromic sulfate, zinc nitrate, aluminum chloride, cupric chromate, ammonium dichrornate and stearate chromium chloride. Of these, oxalic acid, citric acid, ammonium citrate, ammonium oxalate and ammonium chloride are preferred.

The vinyl acetate-based coor terpolymers which form at least a part of the binding matrix in compositions of this invention are preferably combined with the explosive component as aqueous latices, e.g., aqueous dispersions having a solids content of about from 30 to 60 usually about 40-45%. The use of such latices in formulating the compositions of this invention is advantageous since they are commercially available readily and at low cost, eliminate the need of costly or hazardous solvents; and greatly increase the safety of mixing operations wherein the particulate cap-sensitive explosive composition is combined with the copolymer. The water is easily removed by heating, preferably under vacuum. The dried mass is subsequently extruded into the desired physical form, e.g., a cord, and cured by the application of heat.

As mentioned earlier, satisfactory explosive compositions are obtained when a vinyl acetate-based coor terpolymer is the sole binder matrix. However, at least about 15% of total binder, i.e., the vinyl and metallocarboxylate polymer, is required to provide the desired flexibility, abrasion resistance, toughness, and tensile strength to the compositions. However if more than about 55% of elastomeric binder is present the sensitivity of the explosive composition is less than is desired for effective initiation and propagation, particularly in articles of small cross-section or diameter.

Optimum characteristics of toughness and flexibility particularly in compositions to be used as detonating cords and fuse are obtained by employing the vinyl acetatebased coor terpolymers in combination with resins formed by the in situ reaction of a polyvalent metal ion with a copolymer of a 1,3-butadiene hydrocarbon, an acrylic nitrile and an acrylic acid. Typical 1,3-butadiene hydrocarbons used in preparing said copolymers are, for example, 1,3-butadiene and the 5 to 9 carbon atom homologues thereof such as isoprene, 2,3-dimethyl butadiene, l,B-pentanediene-l,3-hexadiene-l,3 and mixtures thereof. As used herein, the term acrylic nitrile refers to acrylonitrile and alpha-substituted acrylonitriles, that is, compounds having the formula:

CH2=(]}-CN Examples of acrylic nitriles are acrylonitrile, methacrylonitrile, ethacrylonitrile, alpha-butylacrylonitrile, alphaphenyl acrylonitrile, alpha-chloroacrylonitrile and alphamethoxymethyl acrylonitrile and mixtures thereof. The

metallocarboxylate polymer can comprise 0 to 50% and weight, that is, 45 parts by weight of free carboxyl groups. The amount of free carboxyl groups in a given copolymer can be determined by titrating a solution of the carboxylic-modified copolymer with alcoholic potassium hydroxide to a phenolphthalein end-point. As used herein, the term acrylic acid refers to acrylic acid and alphasubstituted acrylic acids, that is, compounds having the structural formula:

Acrylic acids which are copolymerized with butadiene- 1,3- hydrocarbons and acrylic nitriles thereby introducing free carboxyl groups into the copolymers are, for example, acrylic acid, methacrylic acid, ethacrylic acid and alphachloro acrylic acid. Copolymers of from 50 to 80% by weight of a butadiene and from about to 45% by weight of an acrylonitrile containing from about 0.001 to 0.3, and especially 0.02 to 0.15, carboxyl equivalent of an acrylic acid per 100 parts by weight of copolymer are preferred. Especially preferred carboxylic copolymers for use in making articles of the present invention are made from 1,3-butadiene, acrylonitrile, and methacrylic acid.

Although said copolymers can be incorporated into the explosive composition by first dispersing them in volatile organic solvents such as aliphatic hydrocarbons, halogenated aliphatic hydrocarbons, toluene, or methyl ethyl ketone, the preferred form of the copolymers is a latex containing from about 35-60% of solids dispersed in an aqueous medium. Such latices present several advantages since latices are the form in which said copolymers are made and, therefore, represent the lowest cost form of the copolymers; no costly and hazardous organic solvents are required to fabricate the articles of this invention; and finally the presence of water in the latex greatly increases the safety of mixing operations wherein a cap-sensitive particulate high explosive is incorporated with the cop lymer, the plasticizer, and the source of polyvalent metallic ion. During mixing the reaction mixture may be heated to slowly remove the water or solvent.

Several grades of said 1,3-butadiene, acrylonitrile, methacrylic acid copolymers can be made, depending upon the ratios of the monomeric molecules which are incorporated in the copolymer. Generally these are described as high, medium, or low acrylonitrile copolymers depending on the proportion of acrylonitrile incorporated in the copolymer, e.g., 50-35%, 35-17%, and l7-l%, respectively for high, medium, and low; and are further characterized by the carboxyl content of the copolymer, as indicated above. For manufacture of articles of the present invention, latices of copolymers of intermediate acrylonitrile content, and carboxyl (-COOH) content of 0.02 to 0.15 part by weight per 100 parts of copolymer, are preferred. Such latices are commercially available as, for example, Hycar 1570X20, 1570X36, 1571 and 1572 (made by the B. F. Goodrich Chemical Co.), of which Hycar 1572 is especially suitable. Such commercially available copolymer latices can be used alone, or in combination with one another or in combination with polyurethane elastomers in order to obtain the physical properties desired in the finished compositions. Adjustments of compositions, curing agents and processing conditions to obtain desired physical properties is Well known in elastomer technology and is regularly practiced by those familiar with elastomer art.

Any source of polyvalent metal ions can be used as a curing agent for the carboxylic copolymer. Polyvalent metal oxides, hydroxides and other sources of polyvalent metal ions such as salts of an acid weaker than acetic acid, and salts of an acid readily eliminated from the crosslinking site, and even finely divided metals, are compounded with, and are used to cure, said carboxylic copolymers by forming the corresponding metallocarboxylate. Representative examples of such metal oxides and other sources of polyvalent metal ion are, for example, zinc oxide, calcium oxide, magnesium oxide, di-

butyltin oxide, lead oxide, barium oxide, cobalt oxide, tin oxide, zinc carbonate, calcium silicate, zinc acetate, sodium aluminate, sodium phosphomolybdate, and mixturesthereof. Zinc oxide is preferred. Usually from about 0.5 to 2 times the chemical equivalent weight of polyvalent metallic oxide, or other source of polyvalent metal iOn, with respect to the amount of carboxyl group in said carboxylic copolymer is used in formulating compositions and articles of this invention.

The carboxylic copolymers which are used in the compositions, and their methods of preparation are described in detail, for example, in US. Patents Nos. 2,395,017 and 2,724,7-07 and are further described in A New High- Strength Elastomer, Rubber World 130, 784-8 (1954); carboxylic Elastorrrers, Industrial and Engineering Chemistry 47, 1006-12 (1955); and Rubber Chemistry and Technology 28, 937 (1955).

The addition of a polyurethane elastomer in amounts to constitute 0 to about 10% and preferably 0 to 8% of the total composition can be especially desirable in explosive compositions which are to be shaped into detonating fuse. Liquid polyurethane elastomers which are characterized by having reactive isocyanate groups by which said liquid polymers can be cured to form solid elastomers, as is well known in the art pertaining to synthetic elastomers, are particularly suitable and are commercially available as, for example, Adiprenes L-100, L-167, L-315, and L-420 which are manufactured by E. I. du Pont de Nemours & Co.

Adiprene L-100 is a liquid polyether urethane elastomer which is made by reacting 1 mole of polytetramethylene ether glycol (PTMEG) of number average molecular weight about 100 with about 1.6 mols of mixed tolylene diisocyanates, as disclosed, for example, in US. Patent Nos. 2,929,800 or 2,948,691. Adiprene L-3 15 also is a liquid polyether urethane elastomer and is made by reacting 1 mol of PTMEG of number average molecular weight about 1000, 1 mol of butanedioll,3 and about 4 mols of mixed tolylene diisocyanate isomers for 4 hours at C. under nitrogen, as disclosed in US. Patent No. 3,188,302. Such liquid polyether urethane elastom'ers sometimes are designated as prepolymers or intermediate polymers because on reaction with curing agents they are cured or vulcanized to form solid elastomers.

Liquid polyurethane elastomers, even when incorporated into compositions of the invention without added curing agents, do cure to some extent and enhance the toughness of the final explosive composition. Preferably, however, curing agents for the liquid polyurethane elastomers also are included in the formulation, as exemplified hereinafter. Said curing agents include diamines, polyols, titanate esters, and others Well known in the art. Diamines are the best general purpose curing agents, and 4,4'-rrrethylenebis(2-chloroaniline), commonly designated MOCA, is preferred. By reaction with said diamine, for example, the liquid polyurethane elastomer is converted to a cured solid polyurethane elastomer which can form a part of the rubbery binder matrix of the explosive compositions and articles of the invention.

A plasticizer can be used in preferred explosive com"- positions of the invention in amounts of about from 0 to 20% by weight to affect the physical and, to some degree, explosive characteristics thereof and to assure that the desired properties are retained over a wide range of environmental conditions, particularly to provide maximum flexibility at low temperatures. Suitable plasticizers can be represented by the general formulas:

i w-0H3)... (I? (C 0 OR) R-O-P-O-R and I O-R (C O O R),

(C O 0R)q 7 in which each R represents an aliphatically saturated hydrocarbon of about 1 to 8 carbon atoms free from functional substituents, i.e., inert in the ssytem,

is a hydrocarbon nucleus of about 1 to 8 carbon atoms, preferably a saturated hydrocarbon, most preferably an acyclic saturated hydrocarbon nucleus, or a benzenoid nucleus, and each of m, n, p, and q is a cardinal number of O or 1, the sum of n, p and q being 2 to 3. (The term ifree of functional substituents mean that the molecules of the organic monohydroxy compound or compounds from which the phosphate and carboxylate esters are derived shall be free of reactive groups other than the OH function.) A representative but not exhaustive group of specific ester plasticizers that can be used effectively either alone or in combinations, includes:

Particularly preferred plasticizers are di-n-butyl phthalate, triethylene glycol-di-ethylhexoate, and diisooctyl adipate which can be used alone or in combination with other plasticizers. Highly aromatic oils can be used in combination with one of the ester plasticizers.

The compositions of this invention are prepared in preferred embodiments by blending, preferably in a mixer of the kneading type, the explosive (which preferably is water-wet for safety in handling), the latex of vinyl acetate-polymer, plasticizer, and various stabilizers, antioxidants, dyes, as desired. The carboxylic copolymer latex and/or the liquid polyurethane elastomer can also be added as desired. The order of adding ingredients is not particularly critical, however addition of particulate high explosive to other ingredients already in the mixing vessel is preferred for reasons of safety. When the carboxylic copolymer latex is employed the source of polyvalent metal ion curing agent therefor is usually the last ingredient added. After initial blending of ingredients has been carried out with the application of heat, e.g., of 70 to 90 F., for about 2 to 10 minutes, vacuum is applied as heating and blending of the mixture are continued until substantially all water is removed from the charge in the mixer. Although vacuum is not essential to effect complete removal of water or other solvents, its use is preferred to speed up processing of the composition. The dried composition is then shaped by pressing into blocks, slabs or sheets, rolled into sheets or films, or extruded into rods, cords, tubes or sheets. After the composition has been formed into the desired shape it is cured. Curing is merely the completion of crosslinking in the vinyl acetate-crotonate copolymer and the reaction of the polyvalent metal ion and carboxylic elastomer, if such are present. This curing may take place at ambient room temperature during storage. However, heating the composition temperature of the particulate, cap-sensitive explosive, reduces the curing time. Curing generally is effected and accelerated at temperatures of about from 70 to C. for about from 8 to 24 hours,

lower temperatures requiring longer curing.

The shaped explosive articles prepared from the composition are elastically extensible and find many uses in the explosive field. Particularly preferred articles prepared from the compositions of this invention are cords, often referred to in the explosive art as detonating fuse. Cords having an explosive loading of 50 to 200 grains/ foot are particularly well suited for applications such as blasting since they present advantages such as high resistance to impact and physical abuse, and remain completely effective even after prolonged exposure to water or extremely high or low temperatures, require no supplementary protective covering and have enhanced initiating or priming power because of the high concentration of explosive at the initiation point and are then free from inert protective coating between the cord and receptor charge. Particularly preferred articles, e.g., detonating fuse, are provided with reinforcing means, e.g., a central core, bound to the explosive composition thus producing an article of great flexibility even at subzero temperatures, little extensibility, and much greater tensile strength than the elastomeric explosive composition.

Any reinforcing element including fine gauge metal wires can be incorporated in the compositions of this invention, however, yarns and threads are preferred for use in detonating fuse. Yarns may be made of cotton, linen, jute, silk, wool, rayon, cellulose esters, nylon, poly(ethylene terephthalate), polyacrylonitrile, glass or other fibers. Spun fiber yarn construction generally is preferred to monofilament threads since a better bond is established between the yarn and the explosive composition; this bond is believed to represent a combination of adhesive and mechanical interlocking forces. Satisfactory bond strength is attained when the tensile strength of the article equals or exceeds the tensile strength of the reinforcing means. The sleeve of the explosive composition should not strip free of the reinforcing means which it surrounds when tension is applied between a representative portion of the article and exposed extensions of the reinforcing means. The reinforcing means can be impregnated with the vinyl acetate based copolymer, the carboxylic elastomer or a combination thereof to increase adhesion between the composition and the reinforcing means. Particularly preferred reinforcing yarns for detonating fuse are textured yarns as described in U.S. Patent 2,783,609 and multiplex yarns as disclosed in copending, coassigned U.S. application Ser. No. 397,139, filed Sept. 17, 1964, now U.S. Patent No. 3,365,872, the teachings of which are incorporated herein by reference. The textured and multiplex yarns have high inherent tensile strength and form a firm bond with the explosive composition. Use of three strands of 5550 denier, 840 filament textured nylon yarn, as described in U.S. 2,783,609 as a reinforcing means in detonating fuse provides a product having a gross tensile strength in excess of lbs.

Reinforcing means can be incorporated in detonating fuse using a ramor screw-type extruder fitted with a cross-head type, circular orifice die which permits extrusion of the elastomeric explosive composition around the reinforcing yarn of thread as it is drawn through the die to form, for example, an elongated cord. If desired, the yarn may be impregnated with the elastomeric composition, which can contain explosive, prior to the extrusion to improve bonding.

For shaped articles in the form of sheets or blocks, individual reinforcing fibers may be dispersed in the explosive mixture before sheeting out, as in calendering, and curing, or yarns can extend linerally parallel to the long dimension of the sheet. Alternatively, the sheeted explosive composition can be calendered onto one or both sides of a latex impregnated woven fabric mesh 9 l and cured, the woven fabric constituting the reinforcing EXAMPLES 2 TO 11 means. Another means of reinforcing the shaped articles of explosive composition of this invention involves wrap- Explosive Compositions of the formulations Shown in ping or braiding reinforcing yarns or threads around an Table 1 are P p and tested as descl'ilfid above, the extruded cord or tube and curing the shaped article. Proportions of yp of Vinyl acrylic COPOIYmeTS being The following examples will further illustrate this Varied ProdllCe Compositions of Varying P y Charinvention. In the examples all parts are by weight except aCtBIiStiCS as s oWn. as noted, The polymeric carboxylate latex, when used i.e., in Examples and 11, is incorporated at the same time EXAMPLE 1 10 as the vinyl acrylic latex, the curing agent therefor being Into a jacketed kneading type mixture fitted with a provided by the zinc oxide added when the composition vacuum tight cover are charged 58 parts of superfine has been blended and essentially freed of moisture. The PETN (average particle size less than ten microns) and polyurethane used is Adiprene L420 added as the 75.25 parts of a latex of a vinyl acetate-based terpolymer liquid monomer. containing 55% of an aqueous phase and 45% solids All the compositions are formed into cords extruded comprising by weight about 55 mole percent polyvinyl around three central reinforcing strands of 5550 denier, acetate, and about 45 mole percent hydroxyethyl acrylate 840 filament textured nylon yarn. All of the cords are and crotonic acid, the latex having a pH of about 4.4 flexible and characterized by good dimensional stability and a viscosity (Brookfield) of 350 cps. and 8.0 parts even at low temperatures of 0 C. and below.

Example 2 3 4 5 6 7 8 9 10 ll Composition:

PETN (superfine) 20 20 20 58 58 58 58 58 58 RDX (superfine) Vinyl Acetate-Crotonate Copolymer:

Composition A 17 l Composition B 2 1 Composition C 5 7 Composition D 4 7 Plasticizer:

Dibutyl phthalate Triethylene glycol di-n-ethy1 hexoate Diisoctyl Adipate Carboxylate latex u. Zinc Oxide Polyurethane MO CA 5 Antioxidant... Dye, Oil Red. 0.15 0.15 0. 15 Detonation Veloc 7, 460 7, 460 7,050 7, 050 6, 520 5, 770 6, 040 6, U00

1 Composition Acomprises polyvinyl acetate and crotonic acid. 11.6;1; these bands identify polyvinyl acetate in the solid component. 2 Composition Bcomprises polyvinyl acetate, hydroxyalkyl acrylate, Also, the spectrum contains a minor absorbance at 5.9;; which is attriand crotonic acid, combined content of hydroxyalkyl acrylate and buted to an aliphatic organic acid, a minor absorbauce at 6.5 is attributed crotonate, 1015%. to a metallic or amine salt of an aliphatic organic acid. A shoulder" at Composition Ccomprises polyvinyl acetate, hydroxyalky acrylate, 6.01.: on the 5.76 t ester band can be attributed to water-interference. The and crotonic acid, combined content of hydroxyalkyl acrylates and spectrum contains no absorption bands which would indicate an arocrotonate, ca. matic or nitrile function. Composition B exhibits an infrared spectrum 4 Composition D-comprises polyvinyl acetate, hydroxyalkyl acrylate, which is basically the same as that of Composition A, but, in addition, and crotonic acid, combined content of hydroxyalkyl acrylates and the spectrum contains absorption bands at 8.51;: and 8.9a. The band at crotonate, ca. 8.51 shows the presence of an acrylate present in an amount correspond- 5 Hycar 1572-addcd as aqueous latex of copolymer of about, by wt., ing to about from 10 to 15% of the solid components of the aqueous latex. 71.4% 1,3-butadiene, 28.5% acrylonitrile, 0.07% methacrylic acid. The band at 8.9;: also shows the presence of an acrylic/ crotonic acid 6 MO CA-methylenebis(O-chloraniline). copolymer. Composition 0 and Composition D are characterized by the 7 These copolymers are identified by infrared analysis as follows: same spectrum as Composition B, but the combined acrylate/crotonate Nora-The spectrum of Composition A is characterized by major contents of these latices are approximately 30% and 45%, respectively. absorption bands at 3.42p, 5.65,, 6.98 7.29;, 8.1 8.9 9.8;, 10.6}l, and

of dibutyl phthalate as plasticizer. The cover is placed I claim:

on the mixer and the mixture is blended for about 5 min- 1. An explosive composition comprising, by weight, utes to assure homogeneity while water at 70-88 C. is about from 45 to 85% of particulate cap-sensitive cryscirculated through the mixer jacket; then 29 inches talline explosive and at least about 15% polymeric binder vacuum or better is applied and mixing continued at therefor, said binder comprising, based on the weight of 71 C. until the mixture is dry. The dry composition is total composition, about from 5 to of a vinyl acetate transferred from the mixer to the barrel of a screw-type based copolymer, made from 50 to 99 mole percent vinyl extruder fitted with a cross-head type, circular-orifice 55 acetate, 0 to about 50% of a polymeric metallocarboxyldie which permits extrusion of the explosive composiate elastomer and 0 to 10% of a polyurethane elastomer, tion about three strands textured nylon yarn (5550 or mixtures thereof, the total binder comprising 15 t0 denier, 840 filament, 0 twist, type N56) each having a 55 by weight of the total composition.

gross tensile strength of about 60 pounds. The barrel is 2. An explosive composition of claim 7 containing 5 at about 18 C. and the die head is at a temperature of 60 to 15 of said vinyl acetate copolymer binder.

about 90 C. The extruded cord, which is partially cured, 3. An explosive composition of claim 7 wherein the is taken up on a reel and stored at 107 C. for 17 hours. vinyl acetate based copolymer binder is made from 1 The fuse has a diameter of 0.186 inch, is unaffected by to 5 mole percent crotonic acid or esters thereof. exposure to water and has a gross tensile strength of 4. An explosive composition of claim 7 wherein the about 180 pounds. The fuse is easily initiated by a cornbinder contains polymeric metallocarboxylate elastomer. mercial blasting cap and detonates at about 6040 5. An explosive composition of claim 8 wherein the meters/sec. The detonating fuse easily actuates a block vinyl acetate based polymeric binder contains 1 to 5 of TNT to which it is attached. The flexibility of the mole percent crotonic acid or esters thereof and up to detonating fuse is demonstrated 'by holding the fuse at 45 mole percent hydroxyalkyl acrylate. -20 F. for about one hour and then wrapping the cord 6. An explosive composition of claim 4 containing up around a Ai-inch-diameter mandrel without fracturing or to 8% of polyurethane elastomer.

cracking the fuse. The center reinforcing yarn is not 7. An explosive composition of claim 1 wherein the stripped from the surrounding explosive composition unvinyl acetate copolymer binder comprises a copolymer der tension up to rupture nor does the yarn cut through of monomers of vinyl acetate and crotonic acid or esters the composition. thereof.

8. An explosive composition of claim 1 wherein the vinyl acetate polymer comprises a terpolymer of monomers of vinyl acetate, crotonic acid or esters thereof, and hydroxyalkyl acrylate.

9. An explosive composition of claim 8 wherein the hydroxyalkyl acrylate contains from 1 to 8 carbon atoms in the alkyl group.

10. An explosive composition of claim 8 wherein the hydroxyalkyl acrylate is hydroxyethyl acrylate.

11. An explosive composition of claim 4 wherein the polymeric metallocarboxylate elastomer is the reaction product of a polyvalent metal ion with a copolymer of butadiene and an acrylic nitrile and an acrylic acid so as to provide about from 0.001 to 0.3 carboxyl equivalents per 100 parts per weight of said butadiene-acrylic nitrile copolymer.

12. An explosive composition of claim 11 containing a plasticizer selected from the group consisting of phosphate esters or carboxylate esters having the formulas wherein R represents an aliphatic saturated hydrocarbon radical having 1 to 8 carbon atoms, H is a hydrocarbon having 1 to 8 carbon atoms and m, n, p and q are cardinal numbers of to 1, the sum of n, p and q being 2 to 3.

13. An explosive composition of claim 12 wherein the plasticizer is dibutyl phthalate.

14. An explosive composition of claim 12 wherein the plasticizer is triethylene glycol di-n-ethyl hexoate.

15. An explosive composition of claim 12 wherein the plasticizer is diisooctyl adipate.

16. An explosive composition of claim 7 wherein the explosive is pentaerythritol tetranitrate.

17. An explosive composition of claim 7 wherein the explosive is cyclotrimethylenetrinitramine.

18. An explosive composition of claim 7 wherein the explosive is cyclotetramethylenetetranitramine.

19. An explosive composition of claim 7 in the form of an elongated cord containing a reinforcing element.

20. An explosive composition of claim 19 wherein the reinforcing element is nylon yarn.

21. A process for fabricating an explosive composition which comprises mixing an aqueous dispersion of, by weight, of the total solids in the composition, about 45 to 85% of particulate cap-sensitive crystalline explosive, about from to 55% of a vinyl acetate based copolymer made from 50 to 99 mole percent vinyl acetate, from 0 to of a liquid polyurethane and from 0 to 50% of an elastomer which is the reaction product of butadiene, an acrylonitrile and a sufiicient amount of an acrylic acid to provide about from 0.001 to 0.3 carboxyl equivalents per 100 parts by weight of copolymer, a source of polyvalent metal ions in an amount chemically equivalent to about 0.5 to 2 times the carboxyl of the butadiene-acrylic nitrile copolymer, or mixtures thereof, and drying the resulting explosive composition.

22. A process of claim 21 wherein the vinyl acetate copolymer added comprises vinyl acetate and crotonic acid or alkyl or hydroxyalkyl ester thereof.

23. A process of claim 22 wherein the vinyl acetate copolymer comprises the reaction product from about to 99 mole percent vinyl acetate and the balance crotonic acid or an alkyl or hydroxyalkyl ester thereof, wherein the alkyl groups contain 1 to 8 carbon atoms.

24. A process of claim 21 wherein the vinyl acetate polymer comprises the reaction product of vinyl acetate,

crotonic acid or esters thereof and hydroxyalkyl acrylate.

25. A process of claim 24 wherein the hydroxyalkyl acrylate is hydroxyethyl acrylate.

26. A process of claim 22 wherein a plasticizer is added to the composition, said plasticizer being selected from the group consisting of phosphate esters or carboxylate esters having the formulas wherein R represents an aliphatic saturated hydrocarbon radical having 1 to 8 carbon atoms, H is a hydrocarbon having 1 to 8 carbon atoms and m, n, p and q are cardinal numbers of 0 to 1, the sum of n, p and q being 2 to 3.

27. A process of claim 22 wherein the particulate crystalline explosive is pentaerythritol tetranitrate.

28. A process of claim 22 wherein the particulate crystalline explosive is cyclotrimethylenetrinitramine.

29. A process of claim 22 wherein the particulate crystalline explosive is cyclotetramethylenetetranitramine.

30. A process of claim 22 with the additional step of extruding the explosive composition through an orifice to form an elongated cord.

31. A process of claim 30 wherein the explosive composition is extruded around a reinforcing element.

32. A process of claim 31 wherein the reinforcing element is nylon yarn.

33. An explosive composition of claim 3 containing 1 to 5 mole percent hydroxyalkyl crotonate.

34. An explosive composition of claim 8 wherein the polymeric metallocarboxylate elastomer is the reaction product of a polyvalent metal ion with a copolymer of butadiene and an acrylic nitrile and an acrylic acid so as to provide about from 0.001 to 0.3 carboxyl equivalents per 100 parts per weight of said butadiene-acrylic nitrile copolymer.

35. An explosive composition of claim 34 containing up to 8% of polyurethane elastomer.

36. An explosive composition of claim 35 in the form of an elongated cord containing a reinforcing element.

37. An explosive composition of claim 36 wherein the reinforcing element is nylon yarn.

38. A process of claim 22 wherein liquid polyurethane is added.

39. A process of claim 38 wherein the particulate crystalline explosive is pentaerythritol tetranitrate.

13 14 40. A process of claim 24 wherein liquid polyurethane 3,147,162 10/ 1964 Paul 149-93 X is added. 3,348,986 10/1967 Sauer.

References Cited UNITED STATES PATENTS BENJAMIN R. PADGETT, Przmary Examimcr. 2,863,353 12/1958 Brimley 861 5 C1. 3,102,833 9/1963 h z 1 1 3 1; 102 70; 149 20; 92, 93; 2 4 3 3,116,186 12/1963 Paul 149-92X UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,428,502 February 18, 1969 William L. Evans It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 11, line 73, after "carboxyl" insert content Signed and sealed this 24th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents 

